302 Valve Springs - How To Change Valvesprings

Once the spring has been removed, it's best to measure the installed height of that particular spring package rather than just guess at the distance between the spring seat and the retainer. A taller installed height reduces both seat and open pressures while a tighter height increases pressure.

If necessary, a tall installed height can be adjusted by using shims to reduce the distance between the spring seat and the retainer. Typically these shims come in 0.015-, 0.030-, and 0.060-inch thicknesses and can be stacked to achieve the desired installed height.

It's also a good idea to check the condition of the oil seal and measure the amount of retainer-to-seal clearance. For example, with a total distance of 0.610 inch, this package can accommodate a 0.560-inch-lift camshaft and still maintain a 0.050-inch minimum clearance.

Once the installed height is properly set and there is plenty of room for the new spring, the spring and retainer can be fitted over the valve stem and compressed in place. Use your fingertips to hold the locks in place and then slowly release the pressure on the spring. Don't worry if the retainer is pulled to one side when fully compressed; if you hold the locks with your fingertips, they generally will direct the retainer into the correct position.

With the locks properly in place, there should be a small gap on one side of the two locks. Remember, locks are designed to be used with a specific valve-stem diameter. Locks designed for a 31/48-inch-stem Rat motor valve will not work on 111/432-inch-stem valves.

Note how the valve on the right has a full-contact pattern across the valve tip while the valve on the left does not.